Various remote spectroscopy methods are already known in the state of the art. One example of such a spectroscopy method is in particular described in application FR 3,039,331.
This spectroscopy method is said to be of the “LIDAR” type, which means that it is carried out by an optical remote detection and measuring tool known under the term “LIDAR”. The term “LIDAR” comes from the expression “light detection and ranging”.
In particular, this method makes it possible to study the composition of a targeted material located at a distance from the LIDAR by emitting a light wave toward this material with a determined frequency, and then receiving a light wave reflected by this material.
Thus, by comparing this reflected light wave with the initial wave or with a reference signal, it is for example possible to determine the absorption coefficient by the material, which generally makes it possible to determine the precise composition of this material.
The light wave is emitted by the LIDAR in the form of a frequency comb generally made up of a plurality of light rays. These rays are generated from a laser signal by one or several modulators with a predetermined frequency, using generating methods known in themselves. This frequency is in particular chosen based on the desired sampling fineness.
All of the rays of the comb are sent simultaneously toward the targeted material, subsequently reflected by this material and received by the LIDAR. By mixing with the reference signal, the received light ray makes it possible to obtain an interferogram of the targeted material. Its Fourier transform then provides a spectrum of the targeted material, i.e., a precise composition of this material.
Each emitted light ray then makes it possible to cover a predetermined wavelength domain by the LIDAR.
However, for certain targeted materials, the wavelength domain of the existing spectroscopy devices is relatively restricted, which does not make it possible to study these materials sufficiently.